Downcomers are commonly used to convey a substance, typically wastewater, from an upper level of a marine vessel to a lower level of the marine vessel along the outside of the vessel's hull. The wastewater is preferably conveyed from either the interior of the marine vessel or its deck to the waterline. “Wastewater” refers to both gray water (water from sink and shower drains) and black water (water from toilet drains). FIGS. 1A and 1B show various prior art downcomers 2 extending along a hull 4 of a marine vessel 6 toward a waterline 8 where the wastewater conveyed by downcomer 2 is discharged. A top 10 of downcomer 2 may extend toward waterline 8 from any level of marine vessel 6. For example, top 10 of downcomer 2 may extend from a deck 14 while a bottom 12 of downcomer 2 may be located close to waterline 8. Such a downcomer may be fed by a deck-mounted scupper or scupper drain extending from deck 14. Alternatively, top 10 of downcomer 2 may be positioned at any location along hull 4 and may extend to any location on hull 4 below top 10 of downcomer 2. The only constraint on where the upper and lower levels are positioned is that the lower level must be physically situated below the upper level. As shown in FIG. 1, the upper level of downcomer 2 may be deck 14 or any location along the vertical axis of hull 4, and the lower level of downcomer 2 may be the waterline or any location along the vertical axis of hull 4. Downcomer 2 may include cap section 16 that extends from hull 4 at an angle. Cap section 16 preferably includes vents 18 that prevent pressure buildup or vacuum formation in downcomer 2. Downcomers attach to the side of marine vessel 6 via fasteners 20 that are spaced along the length of downcomer 2. Typically, of downcomers have a half-pipe shape and are stud-welded to hull 4 of marine vessel 6.
Because of its position on marine vessel 6, downcomer 2 is subject to multiple high-force impacts during harsh docking conditions and collisions with tugboats. When the force of these impacts exceeds the yield strength of downcomer 2, it dents, leaving a permanent deformation. Such deformation must be repaired to maintain a smooth surface and so that wastewater may be efficiently conveyed into the water. Guards 22 are sometimes mounted along the flanks of downcomer 2 to absorb a portion of impacts. Also, guards 22 may protect downcomer 2 from being ripped off of hull 4 during docking of marine vessel 6. However, guards 22 add cost and may not be effective when impact with tugboats or docks occurs above or below guards 22.
Known downcomers are made of steel, presumably due to its high yield strength. However, even steel downcomers can be dented during impact. Repair of a steel downcomer requires that the dented downcomer be removed from the hull and a new undented downcomer be attached in its place. Alternatively, the dented portion of the downcomer can be removed and an undented portion can be rewelded in its place. Both approaches are expensive and time-consuming. Further, downcomers repaired using the second method often experience leaking or an increased incidence of rust or corrosion at the weld.
The outer surface of the downcomer is typically painted so that the downcomer color matches the color of the marine vessel and to delay rust formation. However, maintenance of the painted and/or coated steel downcomers includes regular repainting and general upkeep to prevent rust and corrosion. This regular maintenance is both expensive and time-consuming.
The present inventor has recognized a need for a downcomer that can absorb a substantial amount of energy upon impact without permanently deforming, that is highly resistant to rust and corrosion, that is easily installed and repaired, that is lightweight and hydrodynamic at the water line, and that requires little or no maintenance.